diff --git a/build.js b/build.cjs
similarity index 87%
rename from build.js
rename to build.cjs
index 7e7c997f2..1bb3be17f 100755
--- a/build.js
+++ b/build.cjs
@@ -18,6 +18,11 @@ try {
     // We seem to have it already
 }
 
+/**
+ * @param entryPoint
+ * @param config
+ * @param done
+ */
 function makeBundle(entryPoint, config, done) {
     browserify(entryPoint, config).bundle(function (err, buffer) {
         if (err) {
@@ -39,7 +44,8 @@ makeBundle(
     },
     function (bundle) {
         var script = preamble + bundle;
-        fs.writeFileSync("pkg/sinon.js", script);
+        fs.writeFileSync("pkg/sinon.cjs", script);
+        fs.writeFileSync("pkg/sinon.js", script); // WebWorker can only load js files
     }
 );
 
@@ -53,7 +59,7 @@ makeBundle(
     },
     function (bundle) {
         var script = preamble + bundle;
-        fs.writeFileSync("pkg/sinon-no-sourcemaps.js", script);
+        fs.writeFileSync("pkg/sinon-no-sourcemaps.cjs", script);
     }
 );
 
diff --git a/lib/package.json b/lib/package.json
new file mode 100644
index 000000000..5bbefffba
--- /dev/null
+++ b/lib/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "commonjs"
+}
diff --git a/package.json b/package.json
index 5e8ae5606..da147efe4 100644
--- a/package.json
+++ b/package.json
@@ -43,10 +43,10 @@
     "test-runnable-examples": "docs/release-source/release/examples/run-test.sh",
     "test": "npm run test-node && npm run test-headless && npm run test-webworker && npm run test-esm",
     "check-dependencies": "dependency-check package.json --no-dev --ignore-module esm",
-    "build": "node ./build.js",
+    "build": "node ./build.cjs",
     "build-docs": "cd docs; bundle exec jekyll build",
     "serve-docs": "cd docs; bundle exec jekyll serve --incremental --verbose",
-    "lint": "eslint '**/*.{js,mjs}'",
+    "lint": "eslint '**/*.{js,cjs,mjs}'",
     "pretest-webworker": "npm run build",
     "prebuild": "rimraf pkg && npm run check-dependencies",
     "postbuild": "npm run test-esm-bundle",
@@ -117,6 +117,11 @@
   "browser": "./lib/sinon.js",
   "main": "./lib/sinon.js",
   "module": "./pkg/sinon-esm.js",
+  "exports": {
+    "require": "./pkg/sinon.cjs",
+    "import": "./pkg/sinon-esm.js"
+  },
+  "type": "module",
   "cdn": "./pkg/sinon.js",
   "jsdelivr": "./pkg/sinon.js",
   "esm": {
diff --git a/test/package.json b/test/package.json
new file mode 100644
index 000000000..5bbefffba
--- /dev/null
+++ b/test/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "commonjs"
+}